Silica aerogels represent a distinctive class of porous nanomaterials with increasing importance in biomedical science owing to their ultralow density, extremely high specific surface area, and tunable nano to mesoporous architecture. These materials are commonly fabricated through the removal of the liquid phase from a silica gel while preserving the three-dimensional network, enabling precise control over pore size, surface chemistry, and mechanical properties. Such versatility has driven extensive exploration of silica aerogels for healthcare applications, including controlled drug delivery, tissue engineering scaffolds, biosensors, bioimaging, cancer diagnosis and therapy, wound management, and environmentally relevant biomedical technologies. Nevertheless, successful clinical translation requires careful assessment of biocompatibility, cytotoxicity, biodegradation, and long-term interactions with biological systems. Parameters such as surface silanol density, particle morphology, and degradation behavior critically influence cellular responses and inflammatory outcomes. Recent strategies, including polymer reinforcement, surface functionalization, and composite formation with biopolymers, have demonstrated significant potential to mitigate toxicity while improving mechanical integrity and biological performance. This review provides a comprehensive and up-to-date overview of silica aerogel composites for biomedical applications, emphasizing synthesis approaches, structure-property relationships, and functional performance. Particular attention is given to toxicity mechanisms, regulatory considerations, and design strategies for improved safety and efficacy.
This study investigates the effect of Y addition on the microstructure, tensile properties, and corrosion behavior of high-speed-extruded Mg–5Bi–3Al (BA53) alloy. Y-free BA53 and Y-containing BAW53x alloys (x = 0.2, 0.5, and 1.0 wt.%) are extruded at a die-exit speed of 67 m/min, and the role of Y is examined with emphasis on second-phase evolution and its influence on mechanical and corrosion behavior. Y addition progressively changes the second-phase characteristics from fine intragranular Mg3Bi2 particles to coarse BiY particles concentrated mainly along grain boundaries, while distinct grain refinement appears only at the highest Y content. The tensile yield strength and ultimate tensile strength decrease slightly with increasing Y content, whereas tensile elongation remains comparable and increases slightly at 0.2 wt.% Y. The strength reduction is mainly associated with the reduced strengthening contribution of fine Mg3Bi2 particles. Longitudinal-section observations near the fracture surface show that coarse BiY particles do not act as dominant crack-initiation sites; instead, fracture remains governed mainly by twin-related cracking, which accounts for the limited change in tensile ductility despite the marked change in second-phase characteristics. The corrosion behavior shows a strongly non-monotonic dependence on Y content. A minor addition of 0.2 wt.% Y markedly improves corrosion resistance, whereas larger additions lead to severe deterioration. The Volta potential difference between BiY and the α-Mg matrix is substantially larger than that between Mg3Bi2 and the α-Mg matrix, indicating a stronger local galvanic driving force. Early-stage and cross-sectional corrosion observations further show that BA53 is more susceptible to widespread Mg3Bi2-assisted corrosion initiation, whereas high-Y alloys increasingly develop BiY-assisted localized corrosion, corrosion-front propagation along grain-boundary regions, and corrosion-film instability. These results demonstrate that a minor addition of 0.2 wt.% Y provides a favorable combination of high-speed extrudability, strength–ductility balance, and enhanced corrosion resistance in the present BA53-based alloy system.
The electropulsing anisotropy of pre-twinned AZ31 Mg alloy was investigated via quasi-in-situ electron backscatter diffraction analysis to decouple the thermal and athermal effects of electropulsing treatment. A pre-compression along the rolling direction (RD) introduced extensive {10−12} extension twins, yielding a twinned area fraction of 75.4%. Three consecutive electropulses were applied along the RD or the transverse direction (TD), with the durations tailored to maintain comparable peak temperatures. The TD specimens exhibited higher heating efficiency owing to the predominant a-axis current path preserved in both matrix and twinned regions despite twinning-induced lattice rotation. A finite difference simulation based on the c-axis orientation distribution predicted an electrical resistivity ratio in excellent agreement with the experimental value. Quasi-in-situ tracing revealed that strain-induced boundary migration governed the early stage of microstructural evolution, while nucleation and growth gradually became activated during subsequent cycles; thermally activated twin boundary migration was suppressed under the subsecond thermal exposure. Notably, the RD specimens underwent faster grain growth and twin boundary annihilation than the TD counterparts, contrary to predictions based on grain morphology and texture. This anomalous behavior was ascribed to current crowding in the twinned regions, where the lower resistivity along the c-axis locally amplified the athermal effect, as evidenced by preferential static recovery under a short-duration electropulse. The RD specimens recovered more ductility (up to 71%) than the TD counterparts (19%). This ductility recovery was governed primarily by the deformation behavior associated with the tensile direction and further enhanced by the accelerated microstructural evolution in the RD specimens, which delayed the onset of plastic instability.
